Known in the prior art are programmed switching devices comprising a shaft connected with microswitches by a kinematic linkage, e.g. a cam, and installed in a casing. The shaft has the form of a motion screw with longitudinal splines and carries a nut connected by a pin with a longitudinal guiding cutout in the casing. The cam is connected with the nut by a bearing, while its connection with the screw splines is by means of lobes (see, for example, U.S. Pat. No. 3,721,780).
As the shaft rotates, the nut moves over the motion screw together with the cam. The moving cam presses the actuating elements of the microswitches, the signals of which correspond to certain angular positions of the shaft.
The prior art device fails to ensure delivery of information in any position of the shaft, for example, in the intervals between the positions set by the operation of adjacent microswitches, because the size of these intervals depends on the minimum distance required for mounting the actuating elements of the adjacent microswitches on the path of the cam. Besides, the device does not deliver information about the sign of mismatching between the actual position of the shaft and the position set by the operation of the corresponding microswitch.
Another prior art programmed switching device comprises a main shaft and an intermediate shaft which are interconnected by a worm drive and accommodated in a casing. The intermediate shaft carries a number of cams, each provided with a lobe. Located between the actuating element of each microswitch and the corresponding cam is a tappet articulated to the casing and carrying a roller which rests on the cam surface. The device incorporates a setting mechanism which changes the positions of the main shaft at which the microswitches operate and has a pin located on the intermediate shaft; the cam of the setting mechanism is made in the form of a washer with a central hole for the passage of the intermediate shaft and with holes which interact with the pin under the effect of a spring.
The tappet roller is mounted on a carriage which is connected with the tappet by an adjusting screw and moves along guides. The microswitches are rigidly secured in line on the casing of the device.
During operation of the device, rotation of the main shaft is transmitted by the worm drive to the intermediate shaft and, depending on the turning angle of the intermediate shaft, the cams press the actuating elements of the microswitches via the tappets, thus causing the microswitches to operate. The electric signals of the microswitches, sent at the moment of their operation, determine the positions of the main shaft.
The basic disadvantage of this device lies in its low accuracy, caused by the fact that the main and intermediate shafts are connected by a reduction gearing.